Pulsar Research Articles

A Series of (Net) Spin-down Glitches in PSR J1522–5735: Insights from the Vortex Creep and Vortex Bending Models

Through a detailed timing analysis of Fermi-LAT data, the rotational behavior of the γ-ray pulsar PSR J1522−5735 was tracked from 2008 August (MJD 54692) to 2024 January (MJD 60320). During this 15.4 yr period, two overrecovery glitches and four antiglitches were identified, marking a rare occurrence in rotation-powered pulsars (RPPs). The magnitudes of these (net) spin-down glitches were determined to be ∣Δν g/ν∣ ∼ 10−8, well above the estimated detectability limit. For the two overrecovery glitches, the respective recovery fractions Q are 2.1(7) and 1.4(2). Further analysis showed no substantial variations in either the flux or pulse profile shape in any of these events, suggesting that small (net) spin-down glitches, unlike large events observed in magnetars and magnetar-like RPPs, may occur without leaving an impact on the magnetosphere. Within the framework of the vortex creep and vortex bending models, antiglitches and overrecoveries indicate the recoupling of vortex lines that moved inward as a result of a crustquake; meanwhile, the apparent fluctuations in the spin-down rate after the glitches occur as a result of the coupling of the oscillations of bent vortex lines to the magnetosphere.

X-Ray Hardening Preceding the Onset of SGR 1935+2154's Radio Pulsar Phase

Magnetars are neutron stars with extremely strong magnetic fields, frequently powering high-energy activity in X-rays. Pulsed radio emission following some X-ray outbursts has been detected, albeit its physical origin is unclear. It has long been speculated that the origin of magnetars’ radio signals is different from those from canonical pulsars, although convincing evidence is still lacking. Five months after magnetar SGR 1935+2154's X-ray outburst and its associated fast radio burst 20200428, a radio pulsar phase was discovered. Here we report the discovery of X-ray spectral hardening associated with the emergence of periodic radio pulsations from SGR 1935+2154 and a detailed analysis of the properties of the radio pulses. The observations suggest that radio emission originates from the outer magnetosphere of the magnetar, and the surface heating due to the bombardment of inward-going particles from the radio emission region is responsible for the observed X-ray spectral hardening.

Detection of Hidden Emissions in Two Rotating Radio Transients with High Surface Magnetic Fields

Abstract Rotating radio transients (RRATs) are neutron stars emitting sporadic radio pulses. The unique emission of RRATs has been proposed to resemble those of known pulsar types, such as extreme nulling pulsars or pulsars with giant pulses. However, the presence of additional radiation beyond these sporadic pulses remains unclear. Through high-sensitivity observations and extended tracking, we detected the sequential weak emissions in two RRATs with relatively high surface magnetic fields (B s ∼ 1013 G): J1846-0257 and J1854+0306. These emissions show peak flux densities of 0.15 and 0.41 mJy, up to 687 and 512 times weaker than our detected RRAT single pulses, respectively. The weak emissions contribute small fractions (~16% and 5%) to the total radio pulse energy releases, contrasting significantly with giant-pulse pulsars where normal pulses dominate. Polarization analysis of J1854+0306 suggests that its sporadic RRAT pulses may originate from intermittent enhanced sparking processes due to magnetospheric evolution. Our findings indicate that some RRATs may represent a novel class of pulsars, distinct from any previously known subclass. Further observations of sources with similar rotational properties using high-sensitivity instruments could validate the generality of these hidden emissions.

METHODS OF COMPLEX USE OF ELECTROMAGNETIC WAVES FOR SEARCHING FOR HYDROCARBONS

The study of sounding modes based on the complex use of modulated and radio pulse signals for determining the properties of anisotropic medium above hydrocarbons was carried out. For the frequency modulation mode, regularities in the change in the components of the permittivity tensor of the medium for the right -hand polarization of electromagnetic waves were established with varying modulation parameters. The modulus and phase of the surface impedance components Ż11 and Ż21 were investigated. The revealed manifestations of an abrupt change in the real components of the permittivity tensor component 3  are of practical importance for exploration geophysics. The resonant frequencies and imaginary component for the right-hand polarization of electromagnetic waves of the permittivity tensor of the medium for modulated, dual-frequency and radio pulse signals were calculated. The modeling results can be used in electrical exploration for developing methods and equipment for searching and detecting hydrocarbons.

Millisecond pulsars phenomenology under the light of graph theory

We compute and apply the minimum spanning tree (MST) of the binary millisecond pulsar population, and discuss aspects of the known phenomenology of these systems in this context. We find that the MST effectively separates different classes of spider pulsars ---eclipsing radio pulsars in tight binary systems with a companion of either sim 0.1–0.8 M$_ (redbacks) or $ M$_ in mass (black widows)--- into distinct branches. The MST also separates black widows (BWs) in globular clusters from those found in the field and groups other pulsar classes of interest, including transitional millisecond pulsars (tMSPs). Using the MST and a defined ranking for similarity, we identify possible candidates likely to belong to these pulsar classes. In particular, based on this approach, we propose the BW classification of J1300+1240, J1630+3550, J1317-0157, J1221-0633, J1627+3219, J1737-0314A, and J1701-3006F, discuss that of J1908+2105, and analyze J1723-2837, J1431-4715, and J1902-5105 as possible transitional systems. We introduce an algorithm that quickly locates where new pulsars fall within the MST and use this to examine the positions of the tMSP IGR J18245-2452 (PSR J1824-2452I), the tMSP candidate 3FGL J1544.6-1125, and the accreting millisecond X-ray pulsar SAX J1808.4-3658. Assessing the positions of these sources in the MST ---assuming a range for their unknown variables (e.g., the spin period derivative of PSR J1824-2452I)---, we can effectively narrow down the parameter space necessary for searching for and determining key pulsar parameters through targeted observations.

Exceeding the conformal limit inside rotating neutron stars: Implications to modified theories of gravity

Exceeding the conformal limit inside rotating neutron stars: Implications to modified theories of gravity

Model of spatiotemporal coherent summation of ultra-wideband chaotic radio pulses formed by independent emitters

A model of spatiotemporal summation of ultra-wideband chaotic radio pulses is proposed. The feasibility of using this model for analyzing scenarios of time-coherent radiation from independent sources of ultra-wideband chaotic radio pulses in wireless ultra-wideband systems is substantiated. Two scenarios are considered: where the distance between receiving point and emitters is much greater than the typical size of a group of emitters and where the receiving point is located between the emitters. Distributions of the total pulse energy in space for these scenarios are obtained.

The impact of astrophysical priors on parameter inference for GW230529

ABSTRACT We investigate the effects of prior selection on the inferred mass and spin parameters of the neutron star–black hole merger GW230529_181500. Specifically, we explore models motivated by astrophysical considerations, including massive binary and pulsar evolution. We examine mass and spin distributions of neutron stars constrained by radio pulsar observations, alongside black hole spin observations from previous gravitational-wave detections. We show that the inferred mass distribution highly depends upon the spin prior. Specifically, under the most restrictive, binary stellar evolution models, we obtain narrower distributions of masses with a black hole mass of $4.3^{+0.1}_{-0.1}\ {\rm M}_{\odot }$ and neutron star mass of $1.3^{+0.03}_{-0.03}\ {\rm M}_{\odot }$ where, somewhat surprisingly, it is the prior on component spins that has the greatest impact on the inferred mass distributions. Re-weighting using neutron star mass and spin priors from observations of radio pulsars, with black hole spins from observations of gravitational waves, yields the black hole and the neutron star masses to be $3.8^{+0.5}_{-0.6}$ and $1.4^{+0.2}_{-0.1} \ \mathrm{ M}_\odot$, respectively. The sequence of compact object formation – whether the neutron star or the black hole formed first – cannot be determined at the observed signal-to-noise ratio. However, there is no evidence that the black hole was tidally spun up.

Long-term Study of the 2020 Magnetar-like Outburst of the Young Pulsar PSR J1846-0258 in Kes 75

Magnetar-like activity has been observed in a large variety of neutron stars. PSR J1846−0258 is a young 327 ms radio-quiet pulsar with a large rotational power (∼8 × 1036 erg s−1), and resides at the center of the supernova remnant Kes 75. It is one of the rare examples of a high-magnetic-field pulsar showing characteristics both of magnetars and radio pulsars, and can thus provide important clues on the differences in the emission mechanisms between these two classes. In 2006, PSR J1846−0258 was detected to undergo an outburst for the first time, accompanied by a large flux increase, millisecond X-ray bursts, significant spectral changes, and a large timing glitch. In the period between 2020 May and June, after 14 yr of quiescent stable emission, the source underwent a second magnetar-like outburst, which was followed up with several observations by Neutron Star Interior Composition Explorer, XMM-Newton, NuSTAR, and Swift. In this work, we report on the long-term timing and X-ray spectral properties of the source following the 2020 outburst, and place upper limits on any source activity at radio wavelengths. We demonstrate that the pulsed flux increased by a factor >6 during the outburst, followed by nontrivial variability in the spin-down rate. Our timing analysis shows that the spin frequency and its derivative are clearly affected by magnetospheric activity due to the outburst. We find hints for an oscillation in the frequency derivative with a timescale of 50–60 days, recovering later on to stable quiescence.

Exploring Waveform Variations among Neutron Star Ray-tracing Codes for Complex Emission Geometries

Pulse profile modeling (PPM), the technique used to infer mass, radius, and geometric parameters for rotation-powered millisecond pulsars using data from the Neutron Star Interior Composition Explorer (NICER), relies on relativistic ray-tracing of thermal X-ray photons from hot spots on the neutron star surface to the observer. To verify our ray-tracing codes we have in the past conducted cross tests for simple hot spot geometries, focusing primarily on the implementation of the spacetime model. In this paper, we present verification for test problems that explore the more complex hot spot geometries that are now being employed in the NICER PPM analyses. We conclude that the accuracy of our computed waveforms is in general sufficiently high for analyses of current NICER data sets. We have however identified some extreme configurations where extra care may be needed.

Beyond the Hellings–Downs curve: Non-Einsteinian gravitational waves in pulsar timing array correlations

Pulsar timing arrays (PTAs) have revealed galaxy-size gravitational waves (GWs) in the form of a stochastic gravitational wave background (SGWB), correlating the radio pulses emitted by millisecond pulsars. This discovery naturally leads to the question of the origin and the nature of the SGWB; the latter is synonymous to testing how quadrupolar the inter-pulsar spatial correlation is. In this paper, we investigate the nature of the SGWB by considering correlations beyond the Hellings–Downs (HD) curve of Einstein’s general relativity. We scrutinize the HD and non-Einsteinian GW correlations with the North American Nanohertz Observatory for Gravitational Waves and the Chinese PTA data, and find that both data sets allow a graviton mass of mg ≲ 1.04 × 10−22 eV/c2 and subluminal traveling waves. We discuss gravitational physics scenarios beyond general relativity that could host non-Einsteinian GW correlations in the SGWB and highlight the importance of the cosmic variance inherited from stochastic variations across realizations in interpreting PTA observations.

Pulsar-wind nebulae meeting the circumstellar media of their progenitors

A significative fraction of high-mass stars sail away through the interstellar medium of the galaxies. Once they evolved and died via a core-collapse supernova, a magnetised, rotating neutron star (a pulsar) is usually left over. The immediate surroundings of the pulsar is the pulsar wind, which forms a nebula whose morphology is shaped by the supernova ejecta and channelled into the circumstellar medium of the progenitor star in the pre-supernova time. Irregular pulsar-wind nebulae display a large variety of radio appearances, screened by their interacting supernova blast wave, or harbour asymmetric up–down emission. Here, we present a series of 2.5-dimensional (2 dimensions for the scalar quantities plus a toroidal component for the vectors) black non-relativistic magneto-hydrodynamical simulations exploring the evolution of the pulsar-wind nebulae generated by a red supergiant and a Wolf-Rayet massive supernova progenitor, moving with Mach number $M=1$ and $M=2$ into the warm phase of the Galactic plane. black In such a simplified approach, the progenitor's direction of motion, the local ambient medium magnetic field, and the progenitor and pulsar axis of rotation, are all aligned; this restricted our study to peculiar pulsar-wind nebula of high-equatorial-energy flux. We find that the reverberation of the termination shock of the pulsar-wind nebulae, when sufficiently embedded into its dead stellar surroundings and interacting with the supernova ejecta, is asymmetric and differs greatly as a function of the past circumstellar evolution of its progenitor, which reflects into their projected radio synchrotron emission. This mechanism is particularly at work in the context of remnants involving slowly moving or very massive stars. We find that the mixing of material in plerionic core-collapse supernova remnants is strongly affected by the asymmetric reverberation in their pulsar-wind nebulae.

Interpreting Mass and Radius Measurements of Neutron Stars with Dark Matter Halos

The high densities of neutron stars (NSs) could provide astrophysical locations for dark matter (DM) to accumulate. Depending on the DM model, these DM admixed NSs (DANSs) could have significantly different properties than pure baryonic NSs, accessible through X-ray observations of rotation-powered pulsars. We adopt the two-fluid formalism in general relativity to numerically simulate stable configurations of DANSs, assuming a fermionic equation of state (EOS) for the DM with repulsive self-interaction. The distribution of DM in the DANS as a halo affects the path of X-rays emitted from hot spots on the visible baryonic surface, causing notable changes in the pulse profile observed by telescopes such as NICER, compared to pure baryonic NSs. We explore how various DM models affect the DM mass distribution, leading to different types of dark halos. We quantify the deviation in observed X-ray flux from stars with each of these halos. We identify the pitfalls in interpreting mass and radius measurements of NSs inferred from electromagnetic radiation and constraining the baryonic matter EOS if these dark halos exist.

Теорія фантомізації радіозображень РСА: базові відомості та обґрунтування розмірів ділянки фантомізації

The article's subject of study is the creation of the foundations of the theory of the formation of false elements in the images of aerospace radio vision systems by injecting informational signs of objects absent on the underlying surface. The goal is to substantiate the dimensions of the subsurface areas on which it is possible to simulate objects with different methods of viewing the exploring area from the aerospace radar carrier. Task: to develop the geometry of the problem, which will reflect the interaction between the radar with the synthesis of the Synthetic-aperture radar (SAR) and the radar of phantomization (FR); to develop a general structural diagram of the FR; determine the main parameters, taking into account which will allow planning an "interaction" session between the SAR and the FR; to determine the sizes of the underlying surface areas, where it is possible to provide phantomization of radio images formed by SAR with different methods of examination. The methods used are mathematical and functional analysis, navigation, and remote sensing. The following results were obtained. The geometry of the problem of the interaction between the SAR and the FR was defined; it allowed us to calculate the interaction time between the systems and to establish the law of change of the distance between them at any placement of the SAR in orbit. The influence of the interposition of the considered systems on the expected shape of the SAR sounding signal and the size of the area on which the problem of radio image phantomization arises has been investigated. Examples of calculations of the specified parameters for various types of exploring of the earth's surface by radar from an aerospace carrier are given. Conclusions. The article summarizes and develops the theory of phantom radio images constructed using SAR. The obtained results establishing the dependence between the phantomization geometry and such parameters as the potential and actual time of interaction between the systems, the envelope of the bundle of received radio pulses, and the number of separation bands by range are important for further research in this direction, which at the moment it is advisable to focus on solving the optimization problem phantomization of separate blocks of the radar and determining the conditions for planning the processes of injecting objects into the transmitter signal and into the radio image formed by the SAR.

Differential rotation in neutron stars at finite temperatures

IntroductionThis paper investigates the impact of differential rotation on the bulk properties and onset of rotational instabilities in neutron stars at finite temperatures up to 50 MeV.MethodsUtilizing the relativistic Brueckner-Hartree-Fock (RBHF) formalism in full Dirac space, the study constructs equation of state (EOS) models for hot neutron star matter, including conditions relevant for high temperatures. These finite-temperature EOS models are applied to compute the bulk properties of differentially rotating neutron stars with varying structural deformations.ResultsThe findings demonstrate that the stability of these stars against bar-mode deformation, a key rotational instability, is only weakly dependent on temperature. Differential rotation significantly affects the maximum mass and radius of neutron stars, and the threshold for the onset of bar-mode instability shows minimal sensitivity to temperature changes within the examined range.DiscussionThese findings are crucial for interpreting observational data from neutron star mergers and other high-energy astrophysical events. The research underscores the necessity of incorporating differential rotation and finite temperature effects in neutron star models to predict their properties and stability accurately.

The Galactic population of canonical pulsar. II. Taking into account several evolutionary paths: Interstellar medium interaction, Galactic potential, and a death valley

Pulsars are highly magnetised rotating neutron stars, emitting in a broad electromagnetic energy range. These objects were discovered more than 55 years ago and are astrophysical laboratories for studying physics at extreme conditions. Reproducing the observed pulsar population helps refine our understanding of their formation and evolution scenarios, as well as their radiation processes and geometry. In this paper, we improve our previous population synthesis by focusing on both the radio and gamma -ray pulsar populations, investigating the impact of the Galactic gravitational potential and of the radio emission death line. To elucidate the necessity of a death line, we implemented our refined initial distributions of the spin period and spacial position at birth. This approach allowed us to elevate the sophistication of our simulations to the most recent state-of-the-art approaches. The motion of each individual pulsar was tracked in the Galactic potential by a fourth-order symplectic integration scheme. Our pulsar population synthesis took into account the secular evolution of the force-free magnetosphere and magnetic field decay simultaneously and self-consistently. Each pulsar was evolved from birth to the present time. The radio and gamma -ray emission locations were modelled by the polar cap geometry and striped wind model, respectively. By simulating ten million pulsars, we found that including a death line allows us to better reproduce the observational trend. However, when simulating one million pulsars, we obtained an even more realistic $P- P $ diagram, whether or not a death line was included. This suggests that the ages of the detected pulsars might be overestimated and so, it sets the need for a death line in pulsar population studies into question. Kolmogorov-Smirnov tests confirm the statistical similarity between the observed and simulated $P- P $ diagram. Additionally, simulations with increased gamma -ray telescope sensitivities hint at a significant contribution coming from the gamma -ray pulsars to the GeV excess in the Galactic centre.

Vibrational squeezing via spin inversion pulses

Magnetic resonance force microscopy (MRFM) describes a range of approaches to detect nuclear spins with mechanical sensors. MRFM has the potential to enable magnetic resonance imaging with near-atomic spatial resolution, opening up exciting possibilities in solid state and biological research. In many cases, the spin-mechanics coupling in MRFM is engineered with the help of periodic radio frequency pulses. In this paper, we report that such pulses can result in unwanted parametric amplification of the mechanical vibrations, causing misinterpretation of the measured signal. We show how the parametric effect can be canceled by auxiliary radio frequency pulses or by appropriate post-correction after careful calibration. Future MRFM measurements may even make use of the parametric amplification to reduce the impact of amplifier noise.

An alternative interpretation of magnetars’ traits deduced from the observational data on their outburst fluxes and spectra

ABSTRACT By applying the Efron–Petrosian method to the fluxes S and distances D of the magnetars listed in the Magnetar Outburst Online Catalogue, we show that the observational data are consistent with the dependence $S\propto D^{-3/2}$, which characterizes the emission from the superluminally moving current sheet in the magnetosphere of a non-aligned neutron star, at substantially higher levels of significance than they are with the dependence $S\propto D^{-2}$. This result agrees with that previously obtained by an analysis of the data in the McGill Online Magnetar Catalog and confirms that, contrary to the currently prevalent view, magnetars’ X-ray luminosities do not exceed their spin-down luminosities. The X-ray spectra of magnetars, moreover, are congruous with the spectral energy distribution (SED) of a broad-band non-thermal emission mechanism identical to that at play in rotation-powered pulsars: we show that the SED of the caustics that are generated in certain privileged directions by the magnetospheric current sheet single-handedly fits the observed spectra of 4U 0142+61, 1E 1841−045, and XTE J1810−197 over their entire breadths. Magnetars’ outbursts and their associated radio bursts are predicted to occur when, as a result of large-scale timing anomalies (such as glitches, quakes, or precession), one of the privileged directions along which the radiation from the current sheet decays more slowly than predicted by the inverse-square law either swings past or oscillates across the line of sight.

Stochastic and secular anomalies in pulsar braking indices

ABSTRACT Stochastic and secular variations in the spin frequency $\nu$ of a rotation-powered pulsar complicate the interpretation of the measured braking index, n, in terms of a power-law spin-down torque $\propto \nu ^{n_{\rm pl}}$. Both categories of variation can lead to anomalous braking indices, with $\vert n \vert = \vert \nu \ddot{\nu } / \dot{\nu }^2 \vert \gg 1$, where the overdot symbolizes a derivative with respect to time. Here, we quantify the combined effect of stochastic and secular deviations from pure power-law spin-down on measurements of n. Through analytical calculations, Monte Carlo simulations involving synthetic data, and modern Bayesian timing techniques, it is shown that the variance of n satisfies the predictive, falsifiable formula $\langle n^{2} \rangle = (n_{\rm pl}+\dot{K}_{\rm dim})^{2}+\sigma _{\rm dim}^{2}$, where $\dot{K}_{\rm dim}$ is inversely proportional to the time-scale $\tau _K$ over which the proportionality constant of the power-law spin-down torque varies, $\sigma _{\rm dim}$ is proportional to the timing noise amplitude and inversely proportional to the square root of the total observing time, and the average is over an ensemble of random realizations of the timing noise process. The anomalous regime $\langle n^2 \rangle \gg 1$ occurs for $\dot{K}_{\rm dim} \gg 1$, $\sigma _{\rm dim} \gg 1$, or both. The sign of n depends in part on the sign of $\dot{K}_{\rm dim}$, so it is possible to measure unequal numbers of positive and negative n values in a large sample of pulsars. The distinguishable impact of stochastic and secular anomalies on phase residuals is quantified to prepare for extending the analysis of synthetic data to real pulsars.

TRAPUM pulsar and transient search in the Sextans A and B galaxies and discovery of background FRB 20210924D

ABSTRACT The Small and Large Magellanic Clouds are the only galaxies outside our own in which radio pulsars have been discovered to date. The sensitivity of the MeerKAT radio interferometer offers an opportunity to search for a population of more distant extragalactic pulsars. The TRAPUM (TRansients And PUlsars with MeerKAT) collaboration has performed a radio-domain search for pulsars and transients in the dwarf star-forming galaxies Sextans A and B, situated at the edge of the Local Group 1.4 Mpc away. We conducted three 2-h multibeam observations at L band (856–1712 MHz) with the full array of MeerKAT. No pulsars were found down to a radio pseudo-luminosity upper limit of 7.9$\pm$0.4 Jy kpc$^{2}$ at 1400 MHz, which is 28 times more sensitive than the previous limit from the Murriyang telescope. This luminosity is 30 per cent greater than that of the brightest known radio pulsar and sets a cut-off on the luminosity distributions of the entire Sextans A and B galaxies for unobscured radio pulsars beamed in our direction. A fast radio burst was detected in one of the Sextans A observations at a dispersion measure (DM) of 737 pc cm$^{-3}$. We believe this is a background event not associated with the dwarf galaxy due to its large DM and its signal-to-noise ratio being strongest in the wide-field incoherent beam of MeerKAT.